A VFR C172 PLT DIVERTED TO AN ENRTE ARPT AFTER DETERIORATING WX CONDITIONS PROHIBITED VMC FLT. ATC ATTEMPTED TO GIVE HIM IFR VECTORS INTO IMC.

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I WAS WBND ON A RETURN TRIP. I HAD STOPPED PREVIOUSLY IN ZZZ1 FOR FUEL AND TO REVIEW WX CONDITIONS; WHICH WERE VFR; BUT ICING POTENTIAL; SOME PRECIPITATION. ENRTE; AND AFTER JUST PASSING ZZZ; CONDITIONS WORSENED; ALTHOUGH ATC (I WAS USING 'FLT FOLLOWING') ADVISED ME THAT THERE WERE NO CELLS OF CONVECTIVE ACTIVITY IN MY COURSE DIRECT. GIVEN THE WORSENING CONDITIONS; LIGHT PRECIP THAT STARTED TO FALL; AND DARKER CLOUDS AHEAD THAT LOOKED LIKE THEY WERE DSNDING; I ADVISED ATC THAT I WOULD CHANGE COURSE FOR ZZZ. I MADE A 270 DEG TURN TO THE L; AND THE CTLR ADVISED ME OF A HEADING FOR ZZZ. I INDICATED TO CTR THAT I WOULD HAVE TO DEVIATE IN ORDER TO MAINTAIN VFR; AND HIS REPLY WAS DEVIATE AS REQUIRED. HE PASSED ME OFF TO ZZZ APCH; WHO GAVE ME HEADING AND ALT. THIS HEADING WOULD HAVE TAKEN ME INTO CLOUDS; SO I DEVIATED E. I MAINTAINED THE ALT; 5100 FT. AFTER A COUPLE OF MINS THE APCH CTLR ASKED MY HEADING; I ADVISED HIM 50 DEGS (GPS DIRECT TO ZZZ) AND HE BECAME QUITE UPSET; AND TOLD ME 'YOU ARE NOW IFR; SIR. I GAVE YOU A HEADING 350 DEGS AND YOU STICK TO IT.' I THINK I TOLD HIM AT LEAST ONCE THAT I NEEDED TO MAINTAIN VFR; BUT GOT THE SAME REPLY. I WAS ABLE TO DODGE A FEW CLOUDS WITH MINOR HEADING CHANGES. I DID NOT ENTER IFR CONDITIONS. HE THEN ASSIGNED ME 4700 FT; AND A MORE DIRECT HEADING; AT ABOUT WHICH TIME I GOT THE ARPT IN SIGHT. I WAS TRANSFERRED TO TWR AND MADE A NORMAL LNDG ON RWY 8. THIS CONFUSED ME A GREAT DEAL. I ASKED A COUPLE OF ACR X PLTS I RAN INTO AND AN ACR Y PLT ABOUT THE SIT; AND THEY BOTH RESPONDED THAT THEY HAD NEVER HEARD OF SUCH A THING. I WAS TIRED; WORRIED ABOUT THE PRECIP TURNING TO ICE (IT DID NOT); AND VERY WORRIED ABOUT IFR CONDITIONS AND RISING TERRAIN. THE TRIP WAS SOMEWHAT QUESTIONABLE; WITH HIGH SURFACE WINDS AND A STATIONARY FRONT. I DID HAVE TO DODGE CLOUDS TO MAINTAIN VFR; AND PAY CLOSE ATTENTION TO ICE; BUT I WAS NEVER TOO FAR OUT OF REACH OF A VFR ARPT; WHICH IS WHY I STOPPED IN ZZZ1 AND ZZZ. CAN A CTLR SWITCH A FLT FROM VFR TO IFR WITHOUT REGARD TO THE PLT RATING? THE ARPT WAS ABOVE MINIMUMS; A LEAST FROM THE W SIDE WHERE I WAS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: PLT STATED THAT HE HAD NOT FILED AN IFR FLT PLAN; BUT WAS RECEIVING FLT FOLLOWING. HE WAS VERY CONFUSED ABOUT THE CTLR'S APPARENTLY IFR VECTORS TO THE ARPT AND THE CTLR'S RESPONSE TO HIS INSISTENCE ON MAINTAINING HIS VFR STATUS. HE HAS SINCE RESOLVED THAT THE CTLR COULD NOT ISSUE HIM VECTORS.