PTHF

The melting temperature most often reported for PTHF (see also Tables 2 and 3 for oligomeric glycols) is about 43°C, although these higher values have been observed after annealing. 

It is possible to balance all of these thermodynamic, kinetic, and mechanistic considerations and to prepare well-defined PTHF. Living oxonium ion polymerizations, ie, polymerizations that are free from transfer and termination reactions, are possible. PTHF of any desired molecular weight and with controlled end groups can be prepared. 

Chain Transfer. A number of materials act as tme transfer agents in THF polymerization notable examples are dialkyl ethers and orthoformates. In low concentrations, water behaves as a transfer agent, and hydroxyl end groups are produced. The oxygen of dialkyl ethers are rather poor nucleophiles compared to THF and are therefore not very effective as transfer agents. On the other hand, orthoformates are effective transfer agents and can be used to produce alkoxy-ended PTHFs of any desired molecular weight (169). 

PTHF does not behave ideally in solution and the equiHbrium monomer concentration varies with both solvent and temperature. Kinetics of THF polymerizations fit equation 2, provided that the equiHbrium monomer concentration is deterrnined for the conditions used. 

Block, Gr ft, ndSta.r Copolymers. A host of copolymers of these types have been prepared. They iaclude block copolymers from S-caprolactam and PTMEG as well as block copolymers from PTHF and other cationicaHy polymerizable heterocycles, including... 

Analytical and Test Methods. Most of the analytical and test methods described for THF and PTHF are appHcable to OX and POX with only minor modifications (346). Infrared and nmr are useful aids in the characterization of oxetanes and their polymers. The oxetane ring shows absorption between 960 and 980 cm , regardless of substituents on the ring (282). Dinitro oxetane (DNOX) has its absorption at 1000 cm . In addition, H-nmr chemical shifts for CH2 groups in OX and POX are typically at 4.0—4.8 5 and 3.5—4.7 5, respectively (6,347,348) C-nmr is especially useful for characterizing the microstmcture of polyoxetanes. 

Yijin X. and Caiyaun P., Block and star-hlock copolymers by mechanism transformation. 3. S-(PTHF-PSt)4 and S-(PTHF-PSt-PMMA)4 from living CROP to ATRP, Macromolecules, 33, 4750, 2000. Feldthusen J., Ivan B., and Mueller A.H.E., Synthesis of linear and star-shaped block copolymers of isobutylene and methacrylates hy combination of living cationic and anionic polymerizations. Macromolecules, 31, 578, 1998. 

Figure 5.13 DOSY 2D display for 1 % DBPC in PTHF-1500 (horizontal axis H NMR vertical axis diffusion coefficients). Reproduced by permission of DSM Research, Geleen...

NSE Studies on Entangled Polymer Melts Poly(tetrahydrofurane) (PTHF)... 

Fig. 21. Comparison of the dynamic structure factors from long PTHF chains in a matrix of long chains (x) with that in a matrix of short chains ( ). The Q-value of the experiment was Q = 0.09 A-1, the temperature T = 418 K (Reprinted with permission from [57]. Copyright 1985 Royal Society of Chemistry, Cambridge, UK)...

Particular attention was placed on the crossover from segmental diffusion to the center of mass diffusion at Q 1/Rg and to the monomer diffusion at Q /i, respectively, by Higgins and coworkers [119,120]. While the transition at small Q is very sharp (see Fig. 43, right side), a broader transition range is observed in the regime of larger Q, where the details of the monomer structure become important (see Fig. 44). The experimental data clearly show that only in the case of PDMS does the range 2(Q) Q3 exceed Q = 0.1 A-1, whereas in the case of PS and polytetrahydrofurane (PTHF) it ends at about Q = 0.06-0.07 A-1. Thus, the experimental Q-window to study the internal dynamics of these polymers by NSE is rather limited. 

Symmetric triblock copolymers of the ABA type, where B was PTHF and A poly(2-methyl-2-oxazoline), PMeOx, were prepared by cationic polymerization with trifluoromethanesulfonic anhydride as a difunctional initiator [58]. Subsequent hydrolysis of the PMeOx blocks with HC1 in a methanol/ water mixture resulted in the formation of the corresponding polyethylen-imine blocks (Scheme 20). Samples with relatively low molecular weight distributions were obtained. 

The oxocarbenium perchlorate C(CH20CH2CH2C0+C104 )4 was employed as a tetrafunctional initiator for the synthesis of PTHF 4-arm stars [146]. The living ends were subsequently reacted either with sodium bromoacetate or bromoisobutyryl chloride. The end-capping reaction was not efficient in the first case (lower than 45%). Therefore, the second procedure was the method of choice for the synthesis of the bromoisobutyryl star-shaped macroinitiators. In the presence of CuCl/bpy the ATRP of styrene was initiated in bulk, leading to the formation of (PTHF-fc-PS)4 star-block copolymers. Further addition of MMA provided the (PTHF-fr-PS-fc-PMMA)4 star-block terpolymers. Relatively narrow molecular weight distributions were obtained with this synthetic procedure. 

Benzenetricarbonyl trichloride and l,2,4,5-tetrakis(bromomethyl) benzene were employed as multifunctional initiators for the synthesis of 3-and 4-arm PTHF stars, respectively [147]. The living ends were reacted with sodium 2-bromoisobutyrate followed by reduction with Sml2. The samarium enolates, thus formed were efficient initiators for the polymerization of MMA to give the (PTHF-fo-PMMA) , n = 3 or 4 star-block copolymers, according to Scheme 71. 

The relatively slight broadening of the molecular weight distribution during the polymerization of the MMA blocks showed that the macroinitiator (PTHF)4 is highly efficient in promoting the block copolymerization. 

CDs were found to form inclusion complexes also with poly(tetrahydrofuran) (PTHF) of different molecular weights. In particular, y-CD gave the complexes... 

According to Steiner et al. [69], who studied the complex of /TCD with 1,4-butanediol, a monomer model of PTHF, the crystal packing in this complex is the cage type and isomorphous to that of the jS-CD hydrate, and the methylene chain vibrates in the cavity. However, in the /J-CD-PTHF complex, the polymer chain lays fixed inside a column formed by linearly bonded CD molecules. In agreement with this picture, CP/MAS NMR spectra showed the PTHF chain in the complex to be much less flexible than that in its mixture with the CD. 

---