21 Progress in Polymer Syntheses and Applications HERMAN F. MARK Polytechnic Institute of Brooklyn, 333 Jay St., Brooklyn 1, N. Y.
New polymers can be prepared from new vinyl monomers specially tailored to contain desired functional groups which also appear in the result Downloaded by FUDAN UNIV on January 6, 2017 | http://pubs.acs.org Publication Date: January 1, 1962 | doi: 10.1021/ba-1962-0034.ch021
ing polymer.
Readily available monomers poly
merized and copolymerized by new techniques in which one or more parameters are completely novel or partially modified from previously used ones is still another approach to new macromole cules.
Copolymerization of ethylene with vinyl
-type monomers yields a wide range of plastics, coatings, and adhesives.
Homopolymers of alde
hydes and epoxides as well as copolymers of these two types of monomers range from rigid, highly crystalline to rubbery.
Block and graft copoly
merization leads to elastomeric fibers, while solid state
polymerization
of vinyl
opened up new research vistas.
compounds
has
The salient fea
tures of these reactions are presented and the relations between polymer structure and proper ties are considered with the industrial application in view.
There are, in general, two ways to prepare new polymers w h i c h have valuable and useful properties. O n e of them involves the synthesis of a new monomer, w h i c h embodies b y virtue of its chemical nature some interesting and attractive features. If one then polymerizes such a monomer, one finds i n the polymer the desired properties resulting from repetition of a large number of monomeric units. I n this manner, many new addition polymers have been made from vinyl-type monomers, w h i c h h a d reactive groups such as — C H — C H > , — S H , or — N H C H O H . T h e 2
Ο resulting polymers displayed the reactivity of these functional groups for such purposes as adhesion, solubility, or cross linking. Also, many high temperatureresistant polycondensation products have been prepared b y the use of special aromatic compounds, such as pyromellitic anhydride, naphthalenetetracarboxylic acid, or tetraaminobiphenyl. Another w a y to prepare new polymers w i t h valuable properties is to use well-known, readily available, and usually inexpensive monomers, such as ethylene, 257 PLATZER; POLYMERIZATION AND POLYCONDENSATION PROCESSES Advances in Chemistry; American Chemical Society: Washington, DC, 1962.
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propylene, v i n y l chloride, acrylonitrile, and others, and to subject them to new polymerization techniques, using novel catalysts, activators, promotors, modifiers or unusual combinations of reaction conditions: temperature, pressure, state of aggregation, rate and type of mixing, high energy radiation, etc. Both approaches have been remarkably successful during the past few years i n producing a large number of new and useful polymers i n a l l fields of application and the various articles i n this volume have been skillfully assembled to give a v i v i d picture of the special areas in w h i c h significant progress has already been made. The purpose of this concluding article is to add a few more details to this composite picture because certain recent efforts—basically promising—have i n some cases already reached the new product or process stages or have given, until now, only scattered and incomplete information on the practical application of the resulting materials.
Copolymerization of Ethylene with Vinyl-Type Monomers T h e h i g h pressure polymerization of ethylene can be slightly modified for the copolymerization of ethylene w i t h v i n y l - and acrylic-type monomers such as v i n y l acetate, v i n y l chloride, acrylonitrile, or acrylic esters. Some of these copoly mers of ethylene and v i n y l acetate or maleic anhydride are already available and have found various applications i n plastics, coatings, and adhesives. Copolymers of ethylene and v i n y l chloride and of ethylene and acrylonitrile appear particularly interesting because of the l o w cost of monomers and the properties of the copoly mers. A l t h o u g h their synthesis has been disclosed i n a number of patents their larger scale production is still i n a state of development.
Polymerization of Aldehydes and Epoxides Formaldehyde and other aldehydes can be polymerized under various condi tions to form high molecular weight polymers. Linear polyformaldehyde has been known as D e l r i n for several years. It is a highly crystalline, rigid polymer and has been used already successfully in molding and extrusion. Polyacetaldehyde has been obtained i n an amorphous, atactic form, w h i c h is low melting, readily soluble, and rubbery and i n two stereoregulated forms (isotactic and syndiotactic) w h i c h are crystalline, high melting, and rigid. Copolymers of formaldehyde and acetaldehyde cover the entire range of chemical composition and are rigid and h i g h melting if formaldehyde is i n excess and rubbery if there is an excess of acetaldehyde. T o improve the stability of polyacetals, the end groups have to be protected b y etherification w i t h — C H groups or by esterification w i t h acetic or benzoic acids. Copolymers of aldehydes and epoxides have also been prepared; those of formaldehyde and ethylene oxide are especially interesting as high melting, rigid, and slightly soluble plastics. Polymers and copolymers of epoxides have been obtained recently; they have h i g h molecular weight and interesting properties. T h e rubbery polymers and copolymers of propylene oxide can be cured w i t h sulfur b y introducing a side-chain double bond into the linear macromolecule of the polyether backbone chain b y means of butadiene monoepoxide or glycidyl methacrylate. 3
PLATZER; POLYMERIZATION AND POLYCONDENSATION PROCESSES Advances in Chemistry; American Chemical Society: Washington, DC, 1962.
MARK
Progress in Polymer Synthesis and Applications
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Block and Graft Copolymerization Block copolymerization has given unusual elastomerie fiber formers, w h i c h are used to produce the so-called Spandex-type fibers. Blocks of linear, flexible macromolecules of molecular weight between 1000 and 3000 are prepared and hook together b y means of their reactive e n d groups through reaction w i t h bifunctional molecules w h i c h introduce into the resulting macromolecules (molec ular weight about 20,000) enough stiffness and intermolecular attraction to pro vide a sufficiently h i g h tensile modulus a n d tensile strength. Structures of this type c a n be obtained i n different ways, each of w h i c h , however, offers certain difficulties. T h e first step concerns the chemical nature of the primary blocks, w h i c h are usually of the polyester or polyether type. It w o u l d be very desirable to have hydrocarbon-type primary blocks, but it has not yet been possible to obtain such units w i t h reactive end groups i n a satisfactorily controlled bifunctional arrangement. Polyether blocks w i t h hydroxyl e n d groups are prepared b y the atactic polymerization of tetrahydrofuran or propylene oxide, whence they are rubbery enough for a good elastomer, but are somewhat sensitive to light and oxygen w h i c h , eventually, cause discoloration a n d chemical degradation. A hydroxyl group at the e n d of each chain is easily obtained during polyether forma tion and is accounted for b y the basic reaction mechanism. Rubbery polyester blocks w i t h hydroxyl groups at a l l chain ends can be prepared b y the interaction of adipic or sebacic acids w i t h ethylene or propylene glycols i n the presence of an excess of glycol. If one wants carboxyl groups at a l l chain ends, one works w i t h a corresponding excess of acid, a n d it is not too difficult to get nearly complete bifunctionality. Polyester blocks are stable towards light a n d oxygen but e v i dently are sensitive to hydrolysis. T h e resilience of polyether blocks is superior to that of polyester blocks, particularly at lower temperatures. In order to convert the blocks w i t h a molecular weight of about 2000 to linear macromolecules w i t h molecular weights of 20,000 or more, they are first capped w i t h a diisocyanate—normally of the aromatic type—and then expanded w i t h a diamine or dihydroxy compound. Thus, the principal steps i n the synthesis of elastic fiber molecules are: 1. Preparation of Primary Blocks. HO-fpolyether of 1000 to 3000 molecular weight-}-HO HO HO HOOC-f-polyester of 1000 to 3000 molecular w e i g h t + C O O H 2. Capping of Blocks. OCN-O-NO-CO-O+polyether+O-CO-NH-O-NCO aromatic
Jiisocyanate
3. Expansion of Blocks to Macromolecules. +polyether or p o l y e s t e r + O - C O - N H - O - N H - C O - N H - O - N H - C O - N H - O -
!
I
aromatic diisocyanate aromatic-expander T h e polyether or polyester blocks provide the necessary rubberiness, whereas the accumulation of relatively stiff links w i t h hydrogen bonding capacity between the elastomerie blocks increases resistance to h i g h temperatures a n d the action of solvents. It also increases the modulus of elasticity a n d t h e ultimate tensile strength of the resulting fibers. PLATZER; POLYMERIZATION AND POLYCONDENSATION PROCESSES Advances in Chemistry; American Chemical Society: Washington, DC, 1962.
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Other types of block copolymers are made for use as adhesives and coatings. Considerable efforts have been directed, during the last few years, to graft ing various v i n y l and acrylic monomers on cellulosic fibers or films i n order to modify their properties i n a predetermined way. It was shown that one can graft large amounts of vinyl-type monomers, such as acrylonitrile or acrylic esters on rayon, cotton, cellophane, paper, and wood, thus modifying the properties of the base material i n many respects, and improving, particularly, dimensional stability, water repellency, and resistance to thermal and chemical degradation. Graft copolymers of hexadiene and styrene on elastomers and polyblends of the resulting materials w i t h polystyrene have paved the way for the technology of h i g h impact strength polystyrenes and other high impact strength resin compo sitions w h i c h incorporate many desirable properties to a higher degree not other wise possible without resort to the principle of graft copolymerization. T o obtain successful grafting without too much homopolymer formation very strict control has to be exerted over the compatibility of the various ingredients, the reactivity of the initiators and activators, and the temperature of the reaction. Solid State Polymerization It has long been known that polymerization of nonactivated organic com pounds occurs in the solid crystalline state, but the systematic and scientific study of this phenomenon was only begun a few years ago. T h e principal conditions for a successful polymerization i n the solid crystal line state are: 1. T h e double bonds must be located within the crystal lattice so that they can react w i t h each other without too much displacement and without appreciable lattice distortions. 2. A n initiator of some k i n d must be introduced into the lattice i n sufficient amount to start the growth of chains at a reasonable rate. Both conditions have been explored during recent years and it was found that some monomers such as formaldehyde, acrylonitrile, and certain acrylic esters and salts polymerize very readily, whereas others do not polymerize at all or only to a very small extent. This difference is explained by the special location of the double bonds within the crystal lattices. Initiation of polymerization can be obtained by thermal motion of the crystal lattice (for h i g h melting monomers) or preferably by the use of ionizing radiation, either from h i g h energy sources such as β- and γ-rays or by the use of ultraviolet light and even visible light i n the presence of sensitizers. It is also possible to distribute i n a crystal lattice, at low temperatures, initiating ionic centers, if the monomer is slowly condensed from the vapor phase on a cold plate and single atoms of such materials as lithium, sodium, magnesium, iron, copper, or boron trifluoride, aluminum chloride, and titanium trichloride are added w i t h a molecu lar beam. If composite systems of this k i n d are warmed up, rapid polymerization occurs and almost any k i n d of monomer can be thus converted into a high molecular weight polymer. RECEIVED March 12, 1962.
PLATZER; POLYMERIZATION AND POLYCONDENSATION PROCESSES Advances in Chemistry; American Chemical Society: Washington, DC, 1962.
