Silicones and Silicone-Modified Materials

607 Pages·2000·61.823 MB·English

by  Stephen J. Clarson, John J. Fitzgerald, Michael J. Owen, and Steven D. Smith (Eds.)

Silicones and Silicone-Modified
1 Materials
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In Silicones and Silicone-Modified Materials; Clarson, S., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
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In Silicones and Silicone-Modified Materials; Clarson, S., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
ACS SYMPOSIUM SERIES 729
Silicones and Silicone-Modified
Materials
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k-20 Stephen J. Clarson, EDITOR
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1/ University of Cincinnati
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org 0 | doi: John J. Fitzgerald, EDITOR
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Procter and Gamble Corporation
American Chemical Society, Washington, DC
In Silicones and Silicone-Modified Materials; Clarson, S., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
Library of Congress Cataloging-in-Publication Data
Silicones and silicone-modified materials / Stephen J. Clarson, editor ... [et al.].
p. cm.-(ACS symposium series, ISSN 0097-6156; 729)
Includes bibliographical references and index.
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00 ISBN 0-8412-3613-5
w
29.f 1. Silicones—Congresses.
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0 I. Clarson, Stephen J., 1959- . II. Series.
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In Silicones and Silicone-Modified Materials; Clarson, S., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
Foreword
JLHE ACS SYMPOSIUM SERIES was first published in 1974 to provide
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oped from ACS sponsored symposia based on current scientific re­
search. Occasionally, books are developed from symposia sponsored
by other organizations when the topic is of keen interest to the chem­
istry audience.
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9.f is reviewed for appropriate and comprehensive coverage and for in­
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07 terest to the audience. Some papers may be excluded in order to better
00- focus the book; others may be added to provide comprehensiveness.
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org 0 | doi: poeurssl y apreu bilnischluedd epda pine rst hea rev onlout maecsc.e pVteedrb. atim reproductions of previ­
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In Silicones and Silicone-Modified Materials; Clarson, S., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
Preface
In the early planning discussions that led to the American Chemical Society (ACS) "Silicones
and Silicone Modified Materials" Symposium, we felt that although many meetings had been
held during the 1980s on organosilicon chemistry, no major gathering had been held with the
focus specifically on silicones. Our prediction that such a symposium was much needed was
clearly proven correct by the quantity and quality of the papers presented and by the atten­
dance and interest from the audience during the four full days of oral presentations and also at
the evening poster session in Dallas, Texas.
All major technical symposia are a team effort, so it is a great pleasure to thank Kath­
leen Havelka and Warren Ford for their help, advice, and encouragement throughout the prep­
aration of the symposium. Kathleen had the patience of a saint with our many requests and
"past deadline" updates. Robson Story and his team were their usual efficient and helpful
selves in keeping us on track with the ACS Polymer Preprints. Robert Stackman did an
1
00 outstanding job with coordinated finances and expense claims and deserves our thanks. Dow
9.pr Corning, Gelest, General Electric, Procter and Gamble, and Wacker kindly provided financial
72 assistance and we thank them for helping to make it possible for many of our presenters to
0
0- attend this symposium. From my own team at the University of Cincinnati, we thank Mark
0
0 Van Dyke, Rob Johnston, Jennifer Kearney, Susan Junk, and Melissa Scholle, who each gave
2
k- invaluable assistance with all the various correspondence in both paper and electronic form for
b
1/ both the symposium and this book.
2
0
1 Anne Wilson of the ACS Books Department has been of terrific help at every stage of
0.
1 the commissioning and preparation of this book. We are fortunate to have the ACS Polymer
oi: Preprints for the meeting available for the presenters who were unable to contribute to this
org 0 | d ACS Symposium book. We trust, however, that the various chapters from the symposium that
acs.200 are included here are of interest to the global silicones community. For those colleagues not
pubs.ay 4, awbellec otom ejodi nu su sb aicnk Dfoarll aths ei nS tphrein gS pMrienegt ionfg 1in9 9280, 0w1 ei na rSea nd eDligiehgteod f othr awt hthaet wAeC hSo hpaes wkiilnl dblye
12 | http://n Date: M aSTnEotPhHeEr Nl iJv. eClyL AgRatShOeNri ng of our colleagues from the worldwide silMicIoCnHeAs EcLo mJ. mOWunEiNty .
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uly 16, 2Publicati CDanoedlp latehrgteem Poeofn ltEy nomfg eiMnr eRaeteersirneiaaglr sc hS cCieenntceer and Engineering MMDoaidwill aCCn0odr4, nM1iDnDg1 4,C 8Po6.rOp8.. 6 B-0o9x9 949 4
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University of Cincinnati
Cincinnati, OH 45221-0012
JOHN J. FITZGERALD STEVEN D. SMITH
General Electric Company Silicones Procter and Gamble
260 Hudson River Road, Building 12 Miami Valley Laboratories
Waterford, NY 12188 P.O. Box 538707
Cincinnati, OH 45253-8707
xi
In Silicones and Silicone-Modified Materials; Clarson, S., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
Chapter 1
Overview of Siloxane Polymers
James E. Mark
Department of Chemistry and the Polymer Research Center,
The University of Cincinnati, Cincinnati, OH 45221-0172
([email protected], jemcom.crs.uc.edu)
1
0
0 This review provides coverage of a variety of polysiloxane
h
9.c homopolymers and copolymers, and some related materials. Specific
72 systems include (i) linear siloxane polymers [-SiRR'O-] (with various
0
0- alkyl and aryl R and R' side groups), (ii) sesquisiloxane polymers
00 possibly having a ladder structure, (iii) siloxane-silarylene polymers
2
bk- [-Si(CH3)2OSi(CH3)2(C6H4)m-] (where the phenylenes are either meta
1/ or para), (iv) silalkylene polymers [-Si(CH3)2(CH2)m-], (v)
02 polysiloxanes of exhanced crystallizability through modifications of
1
0. chemical and stereochemical structures, (vi) elastomers from water­
1
oi: -based emulsions, and (vii) random and block copolymers, and blends
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cs.00 resulting polymers in terms of their structures, flexibilities, transition
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12 | http://n Date: M foslofu fiitnd ctse,o rneetlsaat cstti osl mtehneesr, s u,b scoeod oaytf i isnmoglps-,lg asenult rshf,ay acdenr dom lcyoosdnisitf-ricoeolrlnse,dd se-ernepslaaertaaisoteino nst eycsmhtenemmiqsbu. reaAsn ltesoso,
0o convert organosilanes to novel reinforcing fillers within elastomers, and
6, 2cati to ceramics modified by the presence of elastomeric domains for the
uly 1Publi improvement of impact strengths.
J
Of the semi-inorganic polymers, the siloxane or "silicone" polymers have been studied
the most, and are also of the greatest commercial importance {1-13). The present
review provides an overview of some of these polysiloxanes and related materials,
emphasizing their structures, most important and interesting physical properties, and a
variety of their applications.
Siloxane-Type Polymers
Preparation. Polymers of the type [-SiRRO-] are generally prepared by a ring-
x
opening polymerization of a trimer or tetramer (14-19) where R and R can be alkyl or
aryl and x is the degree of polymerization. In this reaction, macrocyclic species are
© 2000 American Chemical Society 1
In Silicones and Silicone-Modified Materials; Clarson, S., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
2
generally formed to the extent of 10-15 wt %. The lower molecular weight ones are
generally stripped from the polymer before it is used in a commercial application.
Their presence is also of interest from a more fundamental point of view, in two
respects. First, the extent to which they occur can be used as a measure of chain
flexibility (20). Second, the separated species can be used to test theoretical predictions
of the differences between otherwise identical cyclic and linear molecules (21). In some
cases, an end blocker such as YR'SiR20SiR2RY is used to give reactive -OSiF^RY
chain ends (22). Polymerization of non-symmetrical cyclics gives stereochemically
variable polymers [-SiRR'O-] analogous to the totally organic vinyl and vinylidene
polymers [-CRR'CH^-]. In principle, it should be possible to prepare them in the same
stereoregular forms (isotactic and syndiotactic) which have been achieved in the case of
some of their organic counterparts. Work of this type is showing great promise (23-
25).
Polymerization of mixtures of monomers can of course be used to obtain random
copolymers. They are generally highly irregular, but now in the chemical rather than
stereochemical sense. Correspondingly, they generally show little if any
1 crystallizability.
0
h0 Some topics involving polymerizations and related chemical reactions which were
9.c covered at the "Silicones and Silicone Modified Materials" symposium are conversions
72 from silicon itself to semi-inorganics (contribution by Lewis), ring-opening
0
0- polymerizations (contributions by Chojnowski, Soum, Kress, Jallouli, and Komuro),
0
0 atom-transfer radical polymerizations (Matyjaszewski), hydrosilation polymerizations
2
k- (Kaganove, Tronc, Narayan-Sarathy), polymerizations with controlled stereochemistry
b
1/ (Kawakami), condensation polymerizations (Fu), and polysilane syntheses (Newton)
2
0 (26).
1
0.
1
oi: Homopolymers.
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acs.200 known, both in the dynamic sense and in the equilbrium sense (20,27-31). Dynamic
ubs.y 4, flexibility refers to a molecule's ability to change spatial arrangements by rotations
pa around its skeletal bonds. The more flexible a chain is in this sense, the more it can be
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skeletal bond, and the fact that the oxygen skeletal atoms are not only unencumbered by
side groups, they are as small as an atom can be and still have the multi-valency needed
to continue a chain structure. Also, the Si-O-Si bond angle of -143° is much more
open than the usual tetrahedral bonding occurring at -110°. In addition, this bond
angle has tremendous deformability. These characteristics also increase the chain's
equilibrium flexibility, which is the ability of a chain to be compact when in the form of
a random coil. This type of flexibility can have a profound effect on the melting point
T of a polymer. In this case, it is the origin of the very low T (-40 °C) of PDMS.
m m
In this regard, crystallization is very important in the case of elastomers, since
crystallites can act as reinforcing agents, particularly if they are strain induced. For this
reason, it is of interest to make siloxane-type backbones with increased stiffness, in an
attempt to increase the T of the polymer. Examples of ways to make a polymer more
m
rigid is to combine two chains into a ladder structure, insert rigid units such as j>
phenylene groups into the chain backbone, or add bulky side groups to the backbone.
Insertion of a silphenylene group [-Si(CH3)2C6H4~] into the backbone of the
PDMS repeat unit yields either the siloxane meta and para silphenylene polymers (32-
38). The T of the former polymer is increased to -48 °C, but no crystallinity has been
g
In Silicones and Silicone-Modified Materials; Clarson, S., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
3
observed to date (36,37). Since the repeat unit is symmetric, it should be possible to
induce crystallinity by stretching. As expected, the g-silphenylene group has a larger
rigidifying effect, increasing T to -18 °C, and giving rise to crystallinity with a T of
g m
148 °C. The resulting polymer is thus a thermoplastic siloxane. Silarylene polymers
having more than one phenylene group in the repeat unit could be of considerable
interest because of the various meta, para combinations that could presumably be
synthesized. It is intriguing that even some flexible siloxane polymers form
mesomorphic (liquid-crystalline) phases (39,40).
Unusual polysiloxane structures that were covered at the symposium are stiffened
chains (Van Dyke, Zhang, Lauter), cyclics (Semlyen, Dagger), ladders and cages (41)
(Crivello, Liehtenham, Feher, Rebrov, Carpenter, Rahimian, Haddad),hyperbranched
structures (Moller, Herzig, Muzafarov, Vasilenko), dendrimers (42,43) (Dvornic,
Owen, Vasilenko, Sheiko, Rebrov), and sheets and tubes (Kenney, Katsoulis) (26).
Permeability. Siloxane polymers have much higher permeability to gases than
1 most other elastomeric materials (44). They have therefore long been of interest for use
0
0 as gas separation membranes, the goal being to vary the basic siloxane structure to
h
9.c improve selectivity without decreasing permeability. Some of the polymers which have
2 been investigated in a major project (45) of this type were: [-Si(CH3)RO-],
7
2000-0 S[-iS(Ci(HC3)H203)-X], Oa~n]d, [[S-iS(Ci(HC36)H25)(RC6OH4-)m]S, i([C-HS3i)(2C0H-]3), 2w(CheHre2) mR- Lis ty[pSiic(aCllyH 3a)2n( CnH-a2)lm-kyl
k- group and X is an n-propyl group made polar by substitution of atoms such as CI or N.
1/b Unfortunately, structural changes that increase the selectivity are generally found to
02 decrease the permeability, and vice versa.
1
0. Another type of membrane designed as an artificial skin coating for burns also
1
oi: exploits the high permeability of siloxane polymers (46). The inner layer of the
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acs.200 provides mechanical support, but also permits outward escape of excess moisture while
ubs.y 4, preventing ingress of harmful bacteria.
pa Soft contact lens prepared from PDMS provide a final example. The oxygen
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Some Unusual Properties of Poly(Dimethylsiloxane). Atypically low
values are exhibited for the characteristic pressure (47) (a corrected internal pressure,
which is much used in the study of liquids), the bulk viscosity r|, and the temperature
coefficient of T|. Also, entropies of dilution and excess volumes on mixing PDMS with
solvents are much lower than can be accounted for by the Flory Equation of State
Theory (47). Finally, as has already been mentioned, PDMS has a surprisingly high
permeability.
Although the molecular origin of these unusual properties is still not known
definitively, a number of suggestions have been put forward. One involves low
intermolecular interactions, and another the very high rotational and oscillatory freedom
of the methyl side groups on the polymer. Still others focus on the chain's very
irregular cross section (very large at the substituted Si atom and very small at the
unsubstituted O atom (47)), or packing problems associated with the alternating large
and more normal bond angles.
In Silicones and Silicone-Modified Materials; Clarson, S., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
4
Surface and Interfacial Properties. The polysiloxanes generally have very
low surface energies (48,49), and considerable research is underway to measure and
control surface and interfacial properties in general. For example, adding fluorine
atoms to the side chains on a polysiloxane backbone should have a marked effect in this
regard (50).
Unusual properties of polysiloxanes that were covered at the symposium are
solubility parameters (Rigby), photoluminescence (Pernisz), formation of mesophases
(51-53) (Godovsky), films (Takahara, Inagaki), and surfaces (Wynne, Owen,
Kowalewski, Jukarainen) (26).
Reactive Homopolymers.
Types of Reactions. In the typical ring-opening polymerization, reactive
hydroxyl groups are automatically placed at the ends of the chains. Substitution
reactions carried out on these chain ends can then be used to convert them into other
functional groups, and these functionalized polymers can undergo a variety of
subsequent reactions. Hydroxy 1-terminated chains, for example, can undergo
1 condensation reactions with alkoxysilanes (54). A difunctional alkoxysilane leads to
0
0 chain extension, and a tri- or tetrafunctional one to network formation. Corresponding
h
9.c addition reactions with di- or triisocyanates represent other possibilities. Similarly,
72 hydrogen-terminated chains can be reacted with molecules having active hydrogen
0
0- atoms (54). A pair of vinyl or other unsaturated groups could also be joined by their
0
0 direct reactions with free radicals. Similar end groups can be placed on siloxane chains
2
k- by the use of an end blocker during polymerization (22). Reactive groups such as
b
1/ vinyls can of course be introduced as side chains by random copolymerizations
2
0 involving, for example, methylvinylsiloxane trimers or tetramers.
1
0. Topics involving functionalized polymers that were covered at the symposium
1
oi: include fluorosilicones (48,50,55) (Narayan-Saratahy), amino acid functionalizations
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cs.00
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0o ends, R* is typically (CH)-5 and Y can be NH, OH, COOH, CH=CH, etc. The
6, 2cati siloxane sequences conta2i3ning these ends ha2ve been joined to oth2er polymeric
July 1 Publi sequePnhcaeses ssuecpha raast iocanrsb, obnlaetnedss, , uarneda sr,e ularetetdh asnuebsj,e acmts id(5e7s,- 6a4n)d ciomviedreesd. at the symposium
involved binodal and spinodal phase separations (Viers), block copolymers (Weber,
McGrath, Yilgor, Gravier), blends (Talmon, Krenceski, Singh, Yilgor, Pearce), and
interpenetrating networks (65) (Boileau, Wengrovius) (26).
Elastomeric Networks. The networks formed by reacting functionally-
terminated siloxane chains with an end linker of functionality three or greater have been
extensively used to study molecular aspects of rubberlike elasticity (32,66,67). They
are "model", "ideal", or "tailor-made" networks in that a great deal is known about their
structures by virtue of the very specific chemical reactions used to synthesize them. For
example, in the case of a stoichiometric balance between chain ends and functional
groups on the end linker, the critically important molecular weight M between cross
c
links is equal to the molecular weight of the chains prior to their end linking. Also, the
functionality of the cross links (number of chains emanating from one of them) is
simply the functionality of the end-linking agent. Finally, the molecular weight
distribution of the network chains is the same as that of the starting polymer, and there
should be few if any dangling-chain irregularities.
Since these networks have a known degree of cross linking (as inversely measured
by M), they can be used to test the molecular theories of rubberlike elasticity,
c
In Silicones and Silicone-Modified Materials; Clarson, S., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.