Caddy, Mark (2001) Modified liquid polysulfide polymers : their preparation, characterisation, photocuring and potential photoapplications. PhD thesis, University of Warwick.

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Abstract

Liquid polysulfide polymers (LPs) H(SCH2CH20CH20CH2CH2S)nH are of wide
commercial importance in the sealants industry. Chemical oxidation of the mercaptan
groups, by inorganic and peroxide catalysts, leads to the formation of durable, flexible
and adhesive elastomers.
Terminal modification of the prepolymers, by substituting a wide range of carbonylcontaining
groups for the thiol protons, has led to the creation of photopolymerisable
oligomers with certain of the desirable properties mentioned above. UV irradiation of
all the modified polysulfides, which exist as viscous oils, resulted in the development
of a solid elastomeric material with considerable powers of adhesion.
The acylation process involves the addition of a slight excess of an acyl halide to the
prepolymer in solution, followed by the addition of an amine to neutralise the HCI
formed. This procedure has been adapted to react di- and polyfunctional termini with
LPs to produce block copolymer polysulfides.
When exposed to UV irradiation, the oligomers slowly photocrosslink, forming an
insoluble elastomer. The increase in degree of polymerisation has been successfully
monitored by 1H NMR spectroscopy; this was achieved by irradiating the oligomers in
NMR tubes containing a thin capillary tube containing a deuterium-lock solvent.
These new materials were characterised by IR, 1H and 13C NMR, GPC, viscometry
and, particularly electrospray and FAB-mass spectrometry. FAB spectra have also
been obtained for the first time for the parent polysulfide as well as the modified
forms; these enable characterisation of the polysulfide backbone and its irregularities.
Characterisation of these cured products has been made by hardness testing, solvent
resistance, flexibility and tensometry. Lap shear measurements have been made of all
of the functionalised cured polysulfides; adhesion is greatly enhanced by the addition
of an adhesion promoter (optimum level 2%). All the systems slowly
photopolymerise without sensitisers or additives, but the addition of radical
photoinitiators shortens the cure time considerably. The modified LPs can be
combined with commercially available polyurethane systems to make a fast curing
photosystem yielding products with excellent adhesion and flexibility.
Each of the modified LPs contains a carbonyl group, which has photoactive potential,
thus excitation of the carbonyl group leads to an n->π* transition to form a reactive
triplet state which then attacks another LP chain to crosslink the polysulfide.
Monitoring of 1H NMR linewidths shows a gradual broadening of lines as
120 Hz
polymerisation proceeds, reaching a plateau value of ΔH1/2=120 Hz, illustrating the elastomeric properties of the polysulfide.
Addition of plasticisers eases the uniform spreading of the oligomers onto sheets
before irradiating, which gives a potential application as a surface coating. Photoresist
imaging agents are another potential application as the modified oligomers act as
negative resists.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Sealing compounds, Sulfides, Thiols, Photopolymerization
Official Date:	August 2001
Dates:	Date Event August 2001 Submitted
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Kemp, T. J. (Terence James), 1938-
Sponsors:	Morton International ; Engineering and Physical Sciences Research Council (EPSRC)
Extent:	xxii, 169 leaves
Language:	eng

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